Factors that affect the outcome of peripheral arterial embolization

Endovascular techniques in the treatment of acute limb ischemia: thrombolytic agents, trials, and percutaneous mechanical thrombectomy techniques

Acute peripheral arterial occlusion is associated with great risk to the patient's limb and life. Failure to restore adequate arterial flow in a timely fashion can result in the development of irreversible tissue infarction and the opportunity for limb salvage is lost. On the other hand, patients with acute limb ischemia are often elderly and frail, and early invasive open surgical procedures without adequate preoperative stabilization and preparation result in an unacceptably high risk of perioperative cardiopulmonary complications and death. Percutaneous methods designed to remove the intraluminal thrombus offer an alternative to immediate open surgical revascularization. These less invasive techniques constitute an option that is better tolerated in medically compromised patients. The causative lesion can be precisely identified and the patency of outflow vessels can be restored. The lesion can then be addressed on an elective basis in a well-prepared patient, using percutaneous or open surgical techniques to effect a durable long-term solution. The treatment options include primary surgical revascularization, thrombolytic therapy, percutaneous mechanical thrombectomy, or a combination of any of the three. Clinicians who themselves have the skills to perform a wide assortment of interventions ranging from percutaneous therapies through open surgical revascularization are best able to arrive at the most rational option for treating a specific clinical scenario. This article is directed at providing the practicing surgeon with a basic fund of knowledge on the diagnostic and therapeutic strategies useful in treating patients with peripheral arterial occlusion. Only in this manner can we expect to reduce the high rate of morbidity and mortality that remains associated with these events.

Current status of thrombolysis for peripheral arterial occlusive disease

Acute peripheral arterial occlusion occurs as a result of thrombosis or embolism. A reduction in the prevalence of rheumatic heart disease accounts for a shift in the frequency of embolic to thrombotic occlusions. Also, a dramatic increase in the number of lower extremity arterial bypass graft procedures explains the predominance of graft occlusions in most recent series of patients with acute limb ischemia. While open surgical procedures remain the gold standard in the treatment of peripheral arterial occlusion, thrombolytic agents have been employed as an alternative to primary surgical revascularization in patients with acute limb ischemia. Systemic administration of thrombolytic agents, while effective for small coronary artery clots, fails to achieve dissolution of the large peripheral arterial thrombi. Catheter-directed administration of the agents directly into the occlusive thrombus is the only means of effecting early recanalization. Prior to 1999, urokinase was the sole agent used in North America for peripheral arterial indications, but the loss of the agent from the marketplace forced clinicians to turn to alternate agents, specifically alteplase and reteplase. Interest in the use of platelet glycoprotein inhibitors and mechanical thrombectomy devices also rose, coincident with the loss of urokinase from the marketplace. Most clinicians welcome the predicted return of urokinase to the marketplace. New investigative trials should be organized and executed to answer some of the remaining questions related to thrombolytic treatment of peripheral arterial disease. Foremost in this regard remains the question of which patients are best treated with percutaneous thrombolytic techniques and which are best treated with primary operative intervention. Ultimately, however, the thrombolytic agents are but one tool in the armamentarium of the vascular practitioner. This review is directed at providing the practicing clinician with the basic fund of knowledge necessary when determining the most appropriate intervention in a particular patient with peripheral arterial occlusion, be it thrombolytic therapy, percutaneous mechanical thrombectomy, primary surgical revascularization, or a combination of the three.

Peripheral arterial disease

Lower extremity peripheral arterial disease (PAD) most frequently presents with pain during ambulation, which is known as "intermittent claudication". Some relief of symptoms is possible with exercise, pharmacotherapy, and cessation of smoking. The risk of limb-loss is overshadowed by the risk of mortality from coexistent coronary artery and cerebrovascular atherosclerosis. Primary therapy should be directed at treating the generalised atherosclerotic process, managing lipids, blood sugar, and blood pressure. By contrast, the risk of limb-loss becomes substantial when there is pain at rest, ischaemic ulceration, or gangrene. Interventions such as balloon angioplasty, stenting, and surgical revascularisation should be considered in these patients with so-called "critical limb ischaemia". The choice of the intervention is dependent on the anatomy of the stenotic or occlusive lesion; percutaneous interventions are appropriate when the lesion is focal and short but longer lesions must be treated with surgical revascularisation to achieve acceptable long-term outcome.

Nonfractionated heparin fails to inhibit arterial thrombosis in a human ex vivo thrombosis model

The effect of nonfractionated heparin on the formation and composition of arterial thrombus is unclear. The purpose of this study in a human ex vivo model was to analyze fibrinoplatelet thrombi and test the inhibitory effect of nonfractionated heparin on arterial thrombus formation. Experiments were carried out in Sakariassen perfusion chambers. Strips coated with either tissue factor (TF) or collagen were exposed to human blood collected from healthy volunteers at an arterial shear stress rate of 2600 s-1 for 1 to 4 min. Platelet deposition was determined using immunoenzymatic techniques to quantify P-selectine, a platelet membrane receptor, in thrombi. Fibrin deposition was determined by quantifying fibrin degradation products released after application of plasmin (D-dimers). Heparin was injected into the blood flow through a blender port system located between the venous puncture site and perfusion chamber. The results of the study showed that in a human ex vivo model, formation of arterial thrombus on two thrombogenic surfaces (tissue factor and collagen) is not inhibited by nonfractionated heparin.

Arterial emboli of the lower limbs: analysis of risk factors for mortality and amputation. Association Universitaire de Recherche en Chirurgie

To evaluate risk factors for mortality and amputation after arterial embolism of the lower limbs, we reviewed the records of 397 patients (201 men [mean age 69 +/- 14 years] and 196 women [mean age 79 +/- 12 years]) who were enrolled in a prospective study. The degree of ischemia was rated as follows: grade I in 26% of patients, grade II in 46%, and grade III in 27%. Among patients with complete obstruction, the emboli were located above the inguinal ligament in 213 limbs (46%), in the superficial or popliteal artery in 196 (43%), and at the infrapopliteal level in four (3%). The emboli were bilateral in 59 cases (15%). In 11% of patients the emboli also involved either an upper limb or a visceral or cerebral artery. The origin of the embolus was the heart in 55% of patients, an artery in 12%, and was unknown in the remaining cases. Two hundred two patients (50%) had arterial fibrillation, 33 (8%) had cardiac conduction abnormalities, 186 (47%) had ischemic heart disease, 55 (14%) had valvular heart disease, and 43 (11%) had cardiac insufficiency. The in-hospital mortality rate was 15% (n = 60) and major amputations or severe ischemic sequelae were observed in 23% (n = 91). Logistic regression analysis revealed four independent preoperative factors associated with a significantly higher risk of death: associated visceral emboli with a relative risk (RR) of 6.7 (p < 0.001), invalidism with an RR of 4.3 (p < 0.001), cardiac insufficiency with an RR of 2.4 (p = 0.001), and creatinemia > 180 ml/L with an RR of 2.1 (p = 0.01). The variables associated with an increased risk of amputation were invalidism (p = 0.001), severity of ischemia (p = 0.001), infrapopliteal location of the embolus (p = 0.001), delay of more than 12 hours before treatment of severe ischemia was initiated (p = 0.01), failure to restore arterial patency (p = 0.001), and postoperative cardiac complications (p = 0.01).

Risk factors for early lower limb loss after embolectomy for acute arterial occlusion: a population-based case-control study

To identify risk factors for lower limb loss after arterial embolectomy a cohort of 1189 patients was studied. Detailed data were obtained for 165 patients who underwent a major amputation within 30 days of embolectomy and for 165 matched controls. The amputation risk was increased in patients with two or more myocardial infarctions (odds ratio (OR) 3.1, 95 per cent confidence interval (CI) 0.8-11.2), chronic ischaemia (OR 2.1, CI 0.9-4.9), long duration of symptoms (OR 4.3, CI 1.9-9.6, for greater than or equal to 25 h versus less than or equal to 6 h) or postoperative heart failure (OR 3.4, CI 1.8-6.5). Reduced risks were found in association with acute myocardial infarction (OR 0.3, CI 0.1-0.9) and postoperative anticoagulation treatment with warfarin (OR 0.3, CI 0.1-0.9). The independent prognostic value of chronic ischaemia and symptom duration, and the beneficial effect of postoperative anticoagulation gained additional support in multivariate analysis. We conclude that the risk of early amputation after arterial embolectomy or thrombectomy can be predicted by several clinical characteristics.

Muscle energy stores in relation to clinical findings and outcome in acute arterial ischaemia of the lower leg

Forty-two patients (mean age 79 years) with acute ischaemia of one leg were evaluated in a prospective study. Forty-nine percent of the patients suffered from embolism, 29% from thrombosis while the etiology was uncertain in 22%. In 30 of the ischaemic legs and in 21 contralateral non-ischaemic legs the muscle energy metabolic status (ATP, ADP, AMP, ECP, PC, Cr and lactate) from the gastrocnemius muscle was measured and compared to values obtained from 24 healthy age-matched controls. There was a high degree of energy metabolic impairment in the ischaemic legs. Furthermore, the contralateral non-ischaemic legs were also energy depleted in comparison with those of the healthy controls. Legs with thrombosis were more energy-deprived than legs with embolism. Clinical evaluation of the degree of ischaemia and the level of occlusion correlated with energy metabolic parameters but the duration of ischaemia did not. The degree of metabolic impairment had no prognostic implication for the clinical outcome.

Patient survival and limb prognosis after arterial embolectomy

Mortality and morbidity after arterial thromboembolectomy were studied in 202 patients. Factors affecting reoperation and survival were identified according to Cox's proportional hazards model. 30-day mortality was 26% and amputation rate 18.5%. NYHA classification was the most important predictor for survival; class 3-4 had a 3.35 times higher death rate than class 1-2. An age greater than 75 years increased the death rate by 2.35 times and the presence of ischaemic heart or peripheral arteriosclerotic disease increased it by 1.69 and 1.65 times, respectively. Symptoms less than or equal to 1 day in duration were associated with a death rate 1.53 times higher than for a longer duration. Reoperation rate was 2.15 times greater in the absence of atrial dysrhythmias. The amputation rate was 3.79 times higher in NYHA class 3-4 than in class 1-2, and 2.47 times higher in the presence of peripheral arteriosclerotic disease. Apparently, thrombosis rather than recurrent embolism is the most important cause of reoperation and amputation. The severity of pre-existing cardiopulmonary disease largely determines prognosis regardless of the severity of the superimposed acute occlusion.

Thromboembolectomy of arteries explored at the ankle

Experience with 11 cases of thromboembolectomy of leg arteries explored at the ankle is presented. Patency was established in 19 of 23 arteries (83%), resulting in salvage of 11 of 14 limbs (79%). This experience documents success of this technique with follow-up ranging from 2 to 70 months (mean followup, 24.7 months). Current indications for the procedure include 1) incomplete extraction of thrombus via the popliteal trifurcation, 2) incomplete transfemoral extraction of thrombus with restoration of a popliteal pulse, and 3) thromboembolus initially confined to the infrapopliteal arteries.

Value of postoperative heparin therapy in peripheral arterial thromboembolism

The experience with 359 patients with arterial thromboembolism from 1963 to 1982 has been reported. Combined operative and anticoagulant therapy appears the most beneficial form of treatment. Treatment with heparin after catheter embolectomy was associated with a decrease in mortality (7.6 percent), number of amputations (5 percent), and recurrent emboli (6 percent). Serious wound complications occurred less frequently than anticipated (8 percent). We advocate prompt arteriography and revascularization procedures to ensure long-term limb function after initial embolectomy for salvage, if the result is less than optimal or expected. Postoperative heparin seems to buy time in marginal cases, enabling secondary operations to ensure a satisfactory outcome in most patients.